The role of the nervous system and ionic factors in the genesis of lethal arrhythmias associated with coronary occlusion will be examined at three levels. First will be the abnormalities in ionic activities produced in ischemic heart muscle, specifically K ion and H ion, second will be the role of these ionic changes in the excitation of cardiac receptors and third will be the effects of left stellectomy and other methods of denervating or blocking the sympathetic efferent cardiac innervation on the reflex arrhythmias engendered by myocardial ischemia. The project titles are: Potassium Loss During Myocardial Ischemia, Mechanisms of Excitation of Cardiac Receptors During Myocardial Ischemia and Left Stellectomy in the Prevention of Sudden Death. The methods to be used include measurements of K ion and H ion, intra- and extracellularly, using ion selective microelectrodes and measurement of unidirectional fluxes of K ion using tracers, development of an in-vitro heart-nerve preparation to record afferent nervous discharge while controlled ionic changes are made and alterations in efferent cardiac innervation in chronic, conscious animals undergoing exercise after one coronary occlusion, during a second coronary occlusion, or during sleep.